Some electronic devices employ fingerprint scanning as a means of user authentication. Fingerprint scanners can be capacitive or optical. Capacitive fingerprint scanners utilize electrical current to sense a fingerprint image by detecting changes in capacitive coupling between ridges and valleys of a fingertip. Optical scanners, in contrast, illuminate the fingertip with light to image light and dark areas corresponding to ridges and valleys of the fingertip.
Many devices with fingerprint sensing technology reserve an external “fingerprint scanning” area on the device that is separate from the display screen. This reservation of space has the effect of limiting a maximum display size. There exist a number of challenges in placing a fingerprint scanner below a full-screen display.